Modelling the response of Arctic and Subarctic marine systems to climate warming

The Arctic and the North Atlantic Oceans are experiencing multiple stresses such as loss of sea ice, changing atmospheric patterns, increasing wind energy at the ocean surface and larger freshwater discharge to coastal regions. To address how the marine system may respond to these stresses I designed and analysed a suite of simulations using a state of the art ocean circulation- sea ice - biogeochemical coupled model. By combining physical oceanography, biogeochemistry and general ecology, this thesis attempts to give an interdisciplinary perspective on the simulated regional changes. The approach was to use sensitivity experiments to isolate the stimuli and the response, and to study the underlying mechanisms leading to the response. I was able to address the impacts of three stresses: large scale atmospheric forcing, stormy wind events, and increasing freshwater discharge. (1) In regard to the sensitivity of deep ocean ventilation to changes in large scale atmospheric patterns like the North Atlantic Oscillation (NAO), I find that ventilation within the deep Labrador Sea is sensitive to the NAO, but unlike previously suggested, the lateral oxygen fluxes dominate the ventilation process over air-sea oxygen fluxes. (2) Windy conditions, which are predicted to increase in the Arctic Ocean, are indeed responsible for a large part of the primary production and biogenic carbon export in the Arctic and Subarctic. The importance of stormy winds is highest in seasonal and ice free regions and lowest in light limited perennial ice regions. (3) The hosing experiments performed to measure the effect of increasing meltwater run-off from the Greenland Ice Sheet revealed that a positive feedback may develop within Baffin Bay with the potential to accelerate melting by bringing warm waters closer to marine terminating glaciers.